The present invention relates to rotary vane pumps, and more particularly to improvements in rotary vane pumps whereby an auxiliary pressure outlet may be provided.
Rotary vane pumps are generally known in the prior art. For example, U.S. Pat. No. 2,544,987, issued Mar. 13, 1951, describes a rotary vane pump of the type generally applicable to the present invention having intake and discharge passages interspersed at approximately 90.degree. intervals about the path of rotation of a rotor. U.S. Pat. No. 2,544,988, issued Mar. 13, 1951 discloses a rotary vane pump having a floating cheek plate and utilizing liquid pressure from the discharge side of the pump against the cheek plate to adjust the clearance between the rotor and vane surfaces and the cheek plate. According to the teachings of this patent the intake passages to the pump are located completely on one side of the rotor of the pumping unit while the discharge passages are completely on the other side of the rotor. The cheek plate is provided with a dual function, providing liquid distributing ports in connecting the discharge side of the pumping unit to the outlet and also directing liquid pressure to the discharge chamber. U.S. Pat. No. 3,007,419, issued Nov. 7, 1961, discloses a rotary vane pump having an accumulator reservoir maintained at a pressure approaching the pump discharge pressure, and valve means operated in phase relation with the pump rotor to bleed small amounts of liquid out of the pump's discharge in a manner to offset pulsations caused by the pump.
U.S. Pat. No. 1,468,889, issued Sept. 25, 1923, discloses a multistage rotary pump having two concentric ported cylinders and an eccentric rotor or rotating member. This patent discloses a plurality of radial vanes confined between two concentric cylinders in a rotor which is eccentrically mounted relative to the cylinders. As the rotor is rotated the vanes are also rotated within the confines of the two concentric cylinders, and the eccentric motion of the rotor creates a relative reciprocation between the rotor and the vanes, so as to provide an inner and outer series of expansible chambers. Passages may interconnect the inner and outer ported cylinders to develop a multistage pumping effect, or liquid may be delivered from the first stage to a comparatively low pressure and from the second stage at a higher pressure. Dual pressure operation is therefore achieved by driving an eccentric rotor within two concentric chambers, and providing complex interrelating passages.
There is a need to provide a pump of relatively simple construction wherein two separate liquid pressures may be delivered from a single pump, particularly where the secondary pump output pressure is independent of the primary pump output pressure. It is preferable to provide such a pump with as simple a design as possible in order that the costs of providing two such pressures may be significantly lower than the cost of merely providing two pumps operating at different pressures and coupled into the same flow system.